An image erasing apparatus has been known in which an image printed on a sheet is erased. The image erasing apparatus erases the image printed on the sheet by decolorizing the image. The image erasing apparatus performs the decolorizing process by, for example, applying heat with respect to a toner forming the image. The image erasing apparatus includes a decolorizing unit and a reading unit. The decolorizing unit applies heat to the sheet to decolorize the image printed on the sheet. The reading unit reads the image so as to store the image before the decolorizing process. The reading unit further reads the image again so as to determine whether or not the decolorizing process is normally performed, after the decolorizing process. Meanwhile, an image forming apparatus has been known in which an image is printed on a sheet using a color erasable toner. The above-described image erasing apparatus may decolorize the image printed on the sheet using the color erasable toner by the image forming apparatus. In addition, the image forming apparatus may print an image onto a reused sheet in which the decolorizing process is performed by the above-described image erasing apparatus.
The above-described image forming apparatus fixes an image of a toner onto the sheet at a predetermined fixing temperature at a first-time printing. The image forming apparatus fixes the toner image onto the sheet at the same fixing temperature even at a multiple-time printing. Here, the first-time printing refers to a case in which an image is printed to a new sheet in which the above-described decolorizing process is not performed, for example. The multiple-time printing refers to a case in which an image is printed to the reused sheet in which the decolorizing process is performed multiple times. In addition, a colorless toner is left on the sheet in which the decolorizing process is performed. Accordingly, a fact that printing is performed multiple times means that the toner is superimposed with respect to the sheet. Thus, when the printing and the decolorizing process are repeatedly performed with respect to the same sheet, physical or chemical properties of the sheet are changed.